NEPHELINE-BEARING ROCKS. 



179 



/ 



Occurrences of- 

 JDoierihic flocks 

 B ft B B 





^ 



C> 



* V 



Fig. 2. 



Petrologically the rocks may be termed dolerites, using 

 the term in its widest possible sense. They are noncrys- 

 talline aggregates of augite and plagioclase with large 

 ilmenite crystals occasionally developed, but owing to the 

 presence or absence of olivine, orthoclase, and nepheline, 

 and the variation in texture, they may fall into the more 

 strictly defined divisions of the olivine dolerites, the essex- 



